This proposal is a resource for the diagnostic and laboratory animal medicine support of the research animal colonies at the Yale School of Medicine. In addition it will support research activities directly related to better defining and understanding diseases of laboratory animals, and conducting preliminary studies to determine if a particular disease is suitable as a model for a human disease. A team approach using the facilities and staff of our clinical chemistry, clinical microscopy, pathology, virology, and laboratory animal medicine units will be employed to accomplish these goals. Standard diagnostic methods as well as electron microscopy, gas chromatography, fluorescent microscopy, and special pathological techniques will be used when applicable. This is an ongoing laboratory and all procedures are well established. Over 200 principal investigators use approximately 200,000 animals annually at this institution. It is essential to the overall research program that diagnostic laboratories and veterinary support be available.